A data center is a specialized facility that provides data serving and backup as well as other network-based services for subscribers and other entities. A data center in its most simple form may consist of a single facility that hosts all of the infrastructure equipment, such as networking and storage systems, servers, redundant power supplies, and environmental controls. Fibre Channel is a high-speed communications technology primarily used to interconnect storage systems and servers in a Storage Area Networks (SAN). Fibre Channel over Ethernet (FCoE) is a standard for encapsulating Fibre Channel traffic within Ethernet frames to, in effect, operate aspects of the SAN over an Ethernet network, which allows data center administrators to drastically reduce cabling among servers and storage systems and also permits server virtualization within the SAN. Fibre Channel technologies are described in “Fibre Channel Backbone-5 Rev. 2.00,” International Committee for Information Technology Standards, Jun. 4, 2009, which is incorporated by reference as if fully set forth herein.
Because Fibre Channel has strict requirements respecting latency and does not employ a native frame retransmission protocol, Fibre Channel traffic requires a very low frame delivery loss rate. As a result, servers employing FCoE use appropriate Ethernet extensions, such as the Ethernet PAUSE mechanism, to reduce congestion within the SAN to provide lossless behavior similar to that provided by native Fibre Channel using a buffer-to-buffer mechanism.
More sophisticated data centers may be provisioned for geographically dispersed organizations using subscriber support equipment located in various physical hosting facilities (sites). As a result, techniques have been developed to extend Fibre Channel across multiple sites to provide storage replication for disaster recovery. Using the FCoE pseudowire model, for example, administrators may extend Fibre Channel links across a wide area Multiprotocol Label Switching (MPLS) network using one or more pseudowires that emulate an FCoE service between the multiple sites. In some implementations, the network devices that terminate a pseudowire for FCoE emulation establishes and maintains the pseudowire according to an FCoE-specific state machine. These termination devices transition among states of the state machine based on messages, exchanged between the termination devices, that indicate congestion within the WAN or overflowing buffer capacity on one or both of the termination devices, for example. For instance, a termination device may direct a remote termination device to cease transmitting FCoE traffic, until directed otherwise, by sending a PAUSE message (e.g., an Alternative Simple Flow Control (ASFC) PAUSE message) over the pseudowire connecting the termination devices.